Marine plastics

It is estimated that about 8 million tonnes of plastic debris is washed into our oceans each year

275 million tonnes of plastic waste are generated every year around the world

Around 90 percent of seabirds are thought to have swallowed plastic

A trillion plastic bags are used each year, which require around 100 million barrels of oil to produce

Less than 5 percent of all plastic waste is recycled

What is plastic?

Plastic is a polymer that is created from processed crude oil and is the world’s most commonly used material. Since its invention in the early 1900s plastic has become extremely popular and its usage has far surpassed that of traditional materials such as wood, paper and glass, which are less durable and versatile and much more expensive.

Over time, society has become more and more reliant on plastic and, in the modern day, it is almost impossible for consumers to avoid it. It is thought that around 275 million tonnes of plastic are produced around the world annually, although this amount is increasing each year. In 2010 alone, Europe was responsible for 57 million tonnes of the global plastic consumption, 39 percent of which was thought to have been used for packaging. The throw-away culture that surrounds plastic has resulted in an exponential increase in the amount of items found in the marine environment, threatening our wildlife, natural habitats and ourselves.

The presence of marine plastics has not only been recorded around coastlines with human populations, they have been found on the most remote islands on Earth and are so widespread that litter can be seen in every marine area, without exception. Despite its usual buoyancy, plastic can be found in all levels of the water column, from the water’s surface to the seafloor. Due to their light weight, plastics can be easily transported by wind and tidal activity, travelling substantial distances from their original source, and for many items of litter, their final destination will be one of the five major ocean gyres.

Despite plastic being produced from organic sources, it does not biodegrade at the same rate as traditional materials. Research has shown that a tin can takes between 50 and 100 years to fully biodegrade on land, whereas it has been estimated that a plastic bag will take over 500 years and some say that it may never fully biodegrade. In marine environments, rather than being broken down by microorganisms, plastic does not degrade and is instead broken down into smaller fragments as it is exposed to light and turbulence until it becomes invisible to the naked eye. When fragments of plastic are broken down to be less than five millimetres, they are known as ‘microplastics’, which are known to cause a different array of environmental issues compared to larger items.

What is the litter?

The Center for Marine Conservation designated a top 12 list of items that are most frequently found in the ocean, which they named the ‘Dirty Dozen’. These consist of:

1) cigarette butts

2) paper pieces

3) plastic pieces

4) styrofoam

5) glass pieces

6) plastic food bags

7) plastic caps and lids

8) metal beverage cans

9) plastic straws

10) glass beverage bottles

11) plastic beverage bottles

12) styrofoam cups

The highest majority of manmade litter within marine ecosystems is believed to originate from the public rather than from fishing vessels or sewage discharges, according to statistics taken from a Marine Conservation Society UK Beach Clean. Plastics can enter the marine ecosystem in many ways, both directly and indirectly.

Direct causes of plastic pollution include fly tipping and illegal dumping by fishing vessels. Despite international law which has made dumping at sea illegal, marine areas are extremely difficult to police and rates of enforcement are extremely low. Shockingly, fishing vessels were legally allowed to dump plastic into the ocean until 1988. In many areas of the world, the lack of sanitation services means that waterways are used as bins, causing mass pollution and creating human health hazards.

Plastic can also enter the marine ecosystem accidentally through indirect human actions. These can occur at sea through fishing vessels accidentally losing gear, ships losing their cargo and items from recreational vessels going overboard. Plastic items left on beaches can easily enter the ocean as the tide comes in or by wind blowing it the short distance from the beach into the water. As litter is emptied into landfill and crushed, items can easily be transported by wind and many will eventually land in a waterway to be transported into the oceans. Despite sewage works being designed to catch as many foreign objects as possible, many are known to pass through the system, eventually reaching the ocean. Microbeads, a type of microplastic, are found in many cosmetic and household cleaning products and as sewage works are unable to filter them out of water, they pass straight into aquatic ecosystems. Microplastics also enter the water system when synthetic fibres are washed in a washing machine, and it is thought that around 1,900 plastic fibres can be produced from washing a single item of synthetic clothing.

How are marine plastics affecting the ocean ecosystem?

Although it is difficult to assess exact figures due to the vast size of our oceans, it has been estimated that over a million marine animals die each year due to the complex array of issues that are caused by plastic pollution in our oceans. Around 300 marine species are thought to be affected by plastic and 65 out of the 120 marine mammals on the IUCN Red List are known to have been entangled in plastic debris. Recent studies have concluded that almost all seabirds and sea turtles have ingested plastic items.

Ingestion

Plastic items floating within the water column or on the water’s surface are frequently mistaken for prey items by sea turtles, fish, marine mammals and birds. Plastic items can become lodged in the digestive system of an animal, causing them to believe that they are not hungry, which can lead to starvation, or can cause blockages that prevent them from eating. Unfortunately, most species are unable to pass plastic items through their digestive system and over time their accumulation can be fatal. An autopsy of a juvenile sperm whale found washed up in 2011 discovered over 100 plastic bags in its stomach, which was ruled as being the cause of its death. Sharply edged plastic items can also cause damage to internal organs which can lead to infections and disease.

Many seabird species mistake plastic items floating on the water’s surface for fish eggs, plankton or other prey, which they eat as well as regurgitating for their chicks. Chicks can encounter the same digestive issues as adults, and the weight of the plastic accumulation can make an individual so heavy that it may never be able to fly.

Plankton forms the most basic level of the marine food web, supporting every species in the ocean. In some areas of the ocean, plastic now outnumbers plankton six to one. Zooplankton are known to feed on microplastics as they are unable to differentiate them from their usual food. With plastic entering the marine food chain at such an early stage, it is believed that almost all marine animals consume plastic. Marine plastics floating on the surface of the water, unlike plankton, block sunlight from penetrating through the water column and prevent photosynthetic organisms such as algae, seagrass and phytoplankton from producing energy. The presence of zooxanthellae, a type of photosyntheticalgae, is crucial for corals to survive, as they produce oxygen for reef-building polyps. If microplastics prevent sunlight from reaching coral reefs, the zooxanthellae cannot photosynthesise, causing polyp mortality and bleaching. These photosynthetic organisms are declining at an alarming rate in many areas where there are high levels of microplastics, which has detrimental effects on the rest of the food chain.

Invertebrate filter feeders such as clams and mussels also have issues with ingesting plastic as their feeding apparatus can easily become blocked by inorganic debris, causing them to starve. Plastics and associated toxins can accumulate in the tissues of filter feeders who can pass these harmful substances on through the food chain.

Marine turtles are especially threatened by ingestion of marine plastics. Their favourite prey, jellyfish, look extremely similar to plastic bags and it is thought that almost all sea turtles have ingested plastic at some point in their life. Over time, plastics accumulated within the gut can trap gas, causing turtles to float involuntarily at the surface of the water and preventing them from diving. This leaves them extremely vulnerable to predation as they cannot seek shelter, prevents them from finding food and puts them at risk of being struck by boats. As plastic can become lodged in the stomach of sea turtles, it can make them feel full so they do not attempt to feed and can starve. Sea turtles cannot regurgitate pieces of plastic due to the downward facing spines in their throat, preventing them from being able to remove any objects from their stomach.

Entanglement

Reports of marine animals that have become entangled in plastic debris have increased tenfold in recent years, with footage and images of victims flooding the internet. Entanglement of marine animals can occur in many plastic items, although the most common offenders are plastic bags, strapping bands, plastic yokes from beverage cans and discarded fishing gear. Nylon gillnets discarded at sea are considered to be one of the most hazardous forms of plastic pollution as their design makes them perfect for trapping fish and other marine life. When these nets continue to catch animals after being discarded, this is known as ‘ghost fishing’.

When an animal becomes entangled in plastic debris, they are often unable to move which can prevent them from eating, resulting in starvation, or in the case of marine mammals and reptiles, it may prevent them from being able to surface for air, causing them to drown. Some individuals may be able to free themselves from the plastic that they become entangled in, but can cause damage to their body in the process which can alter their ability to swim, making them vulnerable to predation. For some individuals who become entangled, the plastic does not cause immediate harm but as they grow, physical malformations can occur and the debris can often become tighter, causing deep lacerations which can easily become infected.

As well as feeding on plastic debris, seabirds also collect plastic items to create nests. The plastic within these nests can easily entangle the adult or the juvenile, causing them to become trapped at the nest site or sustain injuries which could lead to an infection or affect the individual’s ability to fly when the breeding season ends.

Not only do gannets build their nests from plastic material, but they are also known to feed it to their young. The sheer amount of plastic that is in our marine environment is evident at one of the largest gannet breeding colonies, Grassholm Island in Wales, where it is estimated that over 80 percent of the material found within nests contains plastic. Due to the location of Grassholm, its coastline is littered with plastic debris, from fishing lines to toothbrushes. Volunteers visit the island each breeding season in an attempt to free entangled adults and nestlings and attempt to clear some of the litter. Due to gannets having a high level of nest fidelity, volunteers cannot remove nests that contain hazardous plastic items as it may prevent the gannets from breeding the following year, and this would lead to a severe drop in this species’ population size. Instead, the volunteers do all they can to free entangled individuals each breeding season.

Chemical pollution

Plastics in the ocean are known to adsorb toxic chemicals which can cause a multitude of issues for marine life, and those who rely on marine ecosystems for food. The toxins in the ocean come from a variety of sources, both agricultural and industrial, and stick to the surface of large plastic items as well as microplastics, and can enter the marine food chain when an individual mistakes contaminated debris for their usual prey items. There are two common types of organic micropollutants found on the surface of marine plastics, non-phenols and polychlorinated byphenyls, also known as PCBs. Once in the body of an organism these chemicals can cause a lot of physiological harm, with non-phenols disrupting the release of hormones and PCBs impairing growth and development, as well as making an individual more vulnerable to disease. Parabens are also commonly found on the surface of marine plastics, and these chemicals are known to reduce reproduction potential. Plastic items can accumulate these chemicals at a rate up to a million times that of the surrounding water. After ingesting contaminated plastics, the chemicals can bioaccumulate within an individual and if it is eaten, these chemicals are passed up the food chain, eventually reaching human consumers. The concentration of chemicals is so high within certain individuals that their bodies must be disposed of as toxic waste. Despite PCBs being banned internationally in 2002, they are still present in high levels within the marine environment.

The amount of plastic found on our beaches is increasing, presenting a health hazard to local human, plant and animal populations. The microplastics hidden within sand have often accumulated a large amount of harmful chemicals and removing them would be extremely difficult, if not impossible.

Animals at the top of the food chain are those most at risk from the harmful effects of chemical bioaccumulation. In the Arctic, polar bears are at the top of the food chain, consuming a diet of mainly seals, which are known to accumulate high levels of pollutants within their body tissue. The chemicals that polar bears are known to accumulate in high quantities are PCBs, which are known to negatively affect their immune system and leave individuals at risk of contracting infections and diseases such as influenza and herpes. PCBs also reduce the reproductive activities of polar bears as females become masculinised, which can cause a reduction in the size of their reproductive organs and increase aggressive behaviour. Females who do reproduce often have very low milk levels so their offspring are often malnourished and have a higher risk of infant mortality. The impacts of these chemicals could be devastating for the already declining polar bear population, especially as they are very slow reproducers.

Invasive species

Plastics floating through the ocean provide an easy distribution method for invasive species who can attach themselves to the surface of an object. As plastics are lightweight, they are easily transported by tidal activity and therefore have the capacity to transport invasive species thousands of kilometres. There are over 150 invasive species that are believed to have been introduced to areas in this way, most commonly hydroids, bryozoans, bivalve molluscs, barnacles, tube worms and algae.

Invasive species are believed to be one of the greatest threats to biodiversity and have been responsible for the extinction of numerous species around the world. Non-native organisms can often outcompete with local populations for food and shelter, reducing the population size of the native species until it is eventually wiped out.

Invasive species are particularly harmful to island ecosystems due to the high levels of endemic species, which have evolved without the presence of predators or competition. In island ecosystems, species occupy a specific ecological niche and when an invasive species arrives on an island by hitching a ride on plastic debris, the entire food chain can be disrupted.

Human impacts

Not only does plastic pollution have a negative effect on wildlife, but human populations living close to the ocean also suffer. As well as health hazards associated with plastic, the unaesthetically pleasing sight of litter is very off-putting to visitors and tourists and is destroying local economies in many areas of the world. The fishing industry is also being affected, as nets and lines are frequently damaged when debris is captured instead of fish and separating litter from the target catch takes time and effort, costing the industry millions each year. Plastic debris has also been known to puncture holes in the hulls of boats, putting the lives of those on board at risk, as well as becoming entangled in propellers and causing mechanical issues.

Species under threat: humans

As more plastic enters the oceans, more plastic enters the human food chain. As plastic is being ingested by organisms at every level of the food chain, it is likely that the seafood we eat contains high levels of plastic as well as bioaccumulated chemicals and heavy metals. Contaminated fish can be carcinogenic and cause birth defects, decreased immunity to infection and disease and development issues. Scientists are conducting ongoing research to determine the impacts that long term plastic ingestion can have on human health.

Effects of marine plastic

How big is the problem?

Plastic debris can be found in every marine area on Earth, even in places far away from any human life. It is thought that between 1.5 and 4.5 percent of all plastic waste ends up in our oceans.

The North Pacific Ocean gyre is home to the infamous Great Pacific Garbage Patch, which was accidentally discovered by a sailor in 1997 and is comprised of two separate garbage patches linked by a convergence zone, which moves debris between the two patches. Despite the image frequently conjured up by the term ‘Garbage Patch’, the area does not consist of masses of distinguishable plastic items, instead it contains billions of microscopic plastic particles known as ‘microplastics’, which give the water a cloudy appearance that is frequently likened to ‘plastic soup’.

The Great Pacific Garbage Patch is believed to cover an area of almost 700,000 square kilometres, which is roughly the size of Texas, and extends up to 6 metres below the water’s surface. Scientists believe that there are around 3.5 million tonnes of plastic in the Great Pacific Garbage Patch and the amount is set to double over the next 5 years. Despite this being the largest known oceanic garbage patch, there is a similar version in every gyre.

What is already happening to combat plastic pollution?

Laws are being introduced around the world in an effort to combat marine plastic pollution. In the European Union, there are frameworks listed in the Marine Strategy Framework Directive which requires members to monitor and tackle marine litter and all must achieve a ‘good environmental status’ in 2020’s assessment. There are international laws in place which have made dumping at sea illegal, but an overarching international marine plastic law and strategy is needed to ensure that every country around the world is attempting to reduce their contribution to the problem. As plastic bags are one of the most commonly seen litter items in the ocean and are also extremely harmful to terrestrial wildlife, a tax has been introduced in many parts of the world, charging consumers for their usage and drastically decreasing the amount that are being produced.

Pressure has also been put on manufacturers to ensure that their products are contained in recyclable plastic to reduce the amount of plastic waste going into landfill. The USA and Canada banned microbeads from their household and cosmetic products in 2015 and other countries are set to follow in the coming years.

Many companies around the world are developing technology to try and create a device or process which would remove the existing litter from the marine ecosystem without damaging wildlife, but many promising products are still being tested for their ecological safety. Artists and commercial companies have also started developing products from marine litter, including sports shoes, clothing and sculptures.

Conservation organisations such as the Marine Conservation Society and the Ocean Conservancy arrange annual beach cleans where thousands of volunteers remove litter from their local beaches, and record their findings. Many organisations also run other initiatives to reduce plastic consumption and change legislation to protect the oceans from further pollution.

How can we help?

How to help remove or prevent marine litter

Join a beach clean in your local area, or volunteer to clean your local river or canal

Ensure all of your litter is disposed of responsibly and refuse going to landfill is well-contained

Do not flush sanitary items

Report illegal dumping activity

Choose clothing made from natural materials such as organic cotton

Do not partake in balloon or sky lantern releases

Support the campaigns of marine conservation organisations and share them on social media

Do not use products that contain microbeads

Pass on your knowledge to others

How to reduce your plastic usage

Reduce, reuse, recycle

Stop buying bottled water and plastic bags and carry reusable versions with you

Refuse unnecessary plastic straws in cafes or bars

Avoid takeaway meals which usually have plastic containers

Buy your groceries and household products in bulk to reduce the amount of packaging you consume

Glossary

Simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.

Bivalve

A group of aquatic molluscs in which the soft parts are encased in a shell consisting of two parts, known as valves.

Bleaching

A process whereby the coral colonies lose their colour, either due to the loss of pigments by microscopic algae (zooxanthellae) living in symbiosis with their host organisms (polyps), or because these zooxanthellae have been expelled.

Bryozoans

A group of small aquatic animals that form branching, encrusting, or gelatinous moss-like colonies. The colony is comprised of zooids, or individual animals, that each contain a set of internal organs and a crown of tentacles, surrounding the mouth, which is used to gather food.

Hydroids

A group of animals which includes the fresh-water hydras, the marine hydroids, many small jellyfish, a few corals, and the Portuguese man-of-war.

Invertebrate

An animal with no backbone, such as an insect, worm or spider.

Photosynthesise

Metabolic process characteristic of plants in which carbon dioxide is broken down, using energy from sunlight absorbed by the green pigment chlorophyll. Organic compounds are made and oxygen is given off as a by-product.

Photosynthetic

Capable of photosynthesis, a metabolic process characteristic of plants in which carbon dioxide is broken down, using energy from sunlight absorbed by the green pigment chlorophyll. Organic compounds are made and oxygen is given off as a by-product.

Phytoplankton

Aquatic plants, usually tiny, that drift passively with water movements.

Polyp

Typically sedentary soft-bodied component of cnidaria, a group of simple aquatic animals including the sea anemones, corals and jellyfish. A polyp comprises a trunk that is fixed at the base, and a mouth that is placed at the opposite end of the trunk and is surrounded by tentacles.

Polyps

Typically sedentary soft-bodied component of Cnidaria (corals, sea pens etc), which comprise of a trunk that is fixed at the base; the mouth is placed at the opposite end of the trunk, and is surrounded by tentacles.

Zooplankton

Tiny aquatic animals that drift with currents or swim weakly in water.

Zooxanthellae

Single-celled dinoflagellates that form symbiotic relationships with hermatypic ‘reef-building’ corals.